In prior art illuminated key-tops, a light emitting body such as an LED is located behind the display section of each key with characters or symbols on the surface of the key-top.
Also, for thin illuminated keyboard switches, a light guide is provided inside the switch casing such that a reflective surface is located on the bottom surface to reflect light upwards. The light guide made of transparent synthetic resin is arranged with the top surface of the light guide being flat and smooth. The bottom surface of the light guide has a curved surface with the center curving upward. In the curved surface of this sphere or concave are formed concentric small protruding sections. On the top surface of the light guide is a flexible printed board on the stationary side, an insulating film with openings, and a flexible printed board on the movable side, layered in that order. Also on the side of the light guide is an illuminating lamp (see Japanese Utility Model First Publication No. 58-82732).
For devices that have light emitting elements such as a LED behind the display section of each key with a character or symbol on the key-top, the light emitting elements must be prepared and installed for each key-top. Accordingly, the installation work is very troublesome and the light emitting elements themselves are expensive, and thus high cost of the whole device can not be avoided.
There is also a prior art device having a light guide having a flat and smooth top surface and an underneath surface which curves upward in the center with small concentric protruding sections on the curved surface and an illuminating lamp on the side of the light guide, which is constructed such that the top surface of the light guide is generally shone uniformly, which is different from the device where light is shone on only the display section of the corresponding keys. Since the entire top surface of the light guide is generally shone uniformly, the irradiation efficiency is poor. Also the entire underneath surface of the light guide is curved and so it is necessary in its construction to arrange illuminating lamps all around the light guide, causing a problem that the number of illuminating lamps increases.
The object of this invention is to provide a light concentrator which makes it possible to locate a light emitter on only one side of the apparatus while at the same time being able to uniformly illuminate only the display section of the necessary keys.